Percutaneous transluminal coronary angioplasty (PTCA) is a procedure by which a balloon catheter is inserted into and manipulated within a patient's coronary arteries to unblock an obstruction (a stenosis) in the artery. Typically, the catheter is about 150 cm long and is inserted percutaneously into the patient's femoral artery in the region of the groin. The catheter then is advanced upwardly through the patient's arteries to the heart where, with the aid of a guidewire, the catheter is guided into the coronary artery where it can be controlled to perform the angioplasty procedure.
In one type of PTCA catheter, the catheter has two lumens. One lumen, for inflation and deflation of the balloon, extends from a fitting at the proximal end of the catheter and opens distally into the interior of the balloon. The balloon is inflated with a liquid and is deflated by aspirating the liquid from the balloon through the inflation/deflation lumen. The second lumen extends from another fitting at the proximal end of the catheter through the catheter and is open at the distal tip of the catheter shaft. The second lumen is adapted to receive a guidewire, such as the steerable small diameter type of guidewire disclosed in U.S. Pat. No. 4,545,390 (Leary) issued Oct. 8, 1985.
In a typical procedure, the guidewire is preliminarily loaded into the catheter and the assembly is inserted into a previously percutaneously placed guide catheter that extends to the region of the patient's heart and terminates at the entrance to the coronary arteries. The assembly of the balloon angioplasty catheter and the steerable guidewire is advanced through the guide catheter to the entrance to the coronary arteries. The guidewire then is projected into the coronary arteries and is steered by manipulation from its proximal end, while being observed under a fluoroscope, until the guidewire passes through the stenosis in the artery. Once the guidewire is in place, the balloon dilatation catheter is advanced over the guidewire, being thus guided directly to the stenosis so as to place the balloon within the stenosis. Once so placed, the balloon is inflated under substantial pressure to dilate the stenosis.
The anatomy of coronary arteries varies widely from patient to patient. Often a patient's coronary arteries are irregularly shaped and highly tortuous. The tortuous configuration of the arteries may present difficulties to the physician in properly placing the guidewire and then advancing the catheter over the guidewire. A highly tortuous coronary anatomy typically will present considerable resistance to advancement of the catheter over the guidewire. With some types of catheter construction, the increased resistance may cause a tendency for portions of the catheter to collapse or buckle axially. For example, in a catheter having a shaft formed from inner and outer coaxial tubes and a balloon mounted to the distal ends of the tubes, there may be a tendency for the tubes to telescope when presented to an increased resistance. The telescoping of the tubes will tend to draw the ends of the balloon together slightly but sufficiently to permit the balloon to become bunched up as it is forced through the stenosis. The bunching up of the balloon makes it more difficult for the balloon to cross the stenosis. It is among the principal objects of the invention to provide an improved construction for a PTCA catheter, particularly a coaxial catheter, which reduces the tendency for the catheter to telescope and buckle and for the balloon to become bunched up under such axial loads.